The present application relates to an improved damping device which improves the electromagnetic compatibility of components of an electrically driven vehicle.
Electric drives can be used in a vehicle with a hybrid drive or with an exclusively electric drive. In the case of an electric drive, the electromagnetic compatibility (EMC) must be ensured so that other components inside and outside the vehicle are not disrupted.
The measures known from the prior art for improving the electromagnetic compatibility for high-voltage networks in a vehicle with an electric drive are not satisfactory. A conventional EMC filter serves primarily to damp interference signals which are emitted by an active electrical device, for example an inverter, a DC/DC converter and the like. That is to say the function of the filter is to damp a source of interference. In addition to filtered and damped power electronics, a motor vehicle contains further sources of interference which do not always satisfy the requirements of the CE standard. Therefore, in a motor vehicle there may be interference even though the power electronics do not generate any emissions. The resonances in connecting structures, in particular in the cable harnesses, amplify the emissions at certain frequencies. In some configurations, this effect can be significant since the resonances in the connecting structures can cause an interference signal to be radiated by the entire motor vehicle.
Conventional EMC filters do not damp any cable harness resonances which are external with respect to an electrical device.
EP 0 274 347 A1 discloses a series circuit of a resistor and of a capacitor which are each connected between a line and ground.
DE 196 36 816 A1 discloses a ferrite reactor, and discloses that lines are connected to ground via a series circuit composed of a resistor and a capacitor, in order to adapt the wave impedance.
The invention has the object of providing an improved damping device and an improved method for configuring a damping device.
The object of the invention is achieved by a damping device, a motor vehicle having such a damping device, as well as a method of operating the damping device, in accordance with embodiments of the invention.
A damping device according to the invention is designed to damp interference signals in a cable having a plurality of wires and comprises a plurality of first terminals to which the voltage vector U1 is applied and at which the current vector I1 flows, wherein a wire of the cable harness is connected to every first terminal, and a plurality of second terminals to which the voltage vector U2 is applied and at which the current vector I2 flows, wherein a wire of the cable harness is connected to each second terminal. The damping device comprises a first plurality of dipoles Zkk whose first terminal is connected to the wire k and whose second terminal is connected to ground, and optionally a second plurality of dipoles Zkm whose first terminal is connected to the wire k and whose second terminal is connected to the wire m.
The following applies:
            A              _        _              =          (                                                                  A                                  _                  _                                            11                                                                          A                                  _                  _                                            12                                                                                          A                                  _                  _                                            21                                                                          A                                  _                  _                                            22                                          )        ,where the following applies
                    (                                                                              U                  1                                _                                                                                                          I                  1                                _                                                    )            =                        (                                                                                          A                                          _                      _                                                        11                                                                                                  A                                          _                      _                                                        12                                                                                                                          A                                          _                      _                                                        21                                                                                                  A                                          _                      _                                                        22                                                              )                ·                  (                                                                                          U                    2                                    _                                                                                                                          I                    2                                    _                                                              )                      ;                                Y                      _            _                          w            =                                                                  A                                  _                  _                                            21                        ⁢                                          A                                  _                  _                                            12                              -                1                                                    =                  {                      y            km                    }                      ,    k    ,                  m        =                              1            ,            n                    _                    ;      the admittance matrix, and;
Yw the admittance matrix, and;
A is the chain matrix of the cable.
The resistance and the reactance of the dipoles Zkm, Zkk are determined as follows:
      Z          k      ,      m        =      {                                                      -                              1                                  y                                      k                    ,                    m                                                                        ,                          k              ≠              m                        ,                                                                          1              /                                                ∑                                      i                    =                                          1                      :                      n                                                                                                                              ⁢                                                                  ⁢                                  y                                      k                    ,                    i                                                                        ,                          k              =                              m                .                                                        
The cable can be a cable harness, for example a cable harness of an electrically driven motor vehicle. The damping device has the topology of an impedance matrix with a capacitive and an inductive isolation in the lower frequency range which serves to avoid interference with a function in the lower frequency range. The entire circuit of the damping device comprises N!/(2×(N−2)! modal wave impedances which are connected between preferably all the cable wires and all the cable shield sleeves, but a large part of these impedances can be reduced or eliminated, since not all the resonance modes have to be damped.
One of the wires of the cable can be a first shield which shields at least one other wire. The first shield can be connected to ground via a dipole Zkk, and the wires of the cable can each be connected to the first shield via a dipole Zkm. In another embodiment, the first shield can be connected to a second shield via a dipole Zkk and the wires of the cable can each be connected to the first shield via a dipole Zkm. The electromagnetic behavior of the cable and of the electrical devices connected thereto can be improved by the shields and the shielding of individual wires or of a plurality of wires by means of a shield. The damping device can have an inductance which is connected to a wire of the cable. In particular, the inductance can be connected in series with the wire. Alternatively or additionally, the damping device can have a component which acts as an inductance, for example an SMD ferrite or a CM core, and is arranged around a plurality of wires of the cable. Alternatively to this or in addition, the damping device comprises a component which acts as an inductance and is arranged around all the wires of the cable apart from the second shield.
If the modal wave impedances are greater than or comparable to input impedances, SMD ferrites or CM/DM ferrite cores can be used for the inductive isolation. This ensures that the input impedances which are connected in parallel cannot influence the damping of the resonance. The selection of a specific isolation measure depends on the different types of filter and on the EMC filter concept which is used.
The invention also relates to a motor vehicle having an electric drive and the damping device described above.
The first shield can be a cable harness ground, and the second shield can be a housing shield which is connected to the bodywork.
In another embodiment, the dipoles Zkk can be connected to the first shield and each wire can be coupled to the first shield by means of a second capacitance, wherein in every wire an inductance is connected between the dipole and the second capacitance. This type of wave damping is advantageous, in particular, in the case of a low-voltage signal cable harness.
In comparison with the wave impedances in the frequency range in which the cable resonances take place, the inductance preferably has a high resistance, and the capacitor preferably has a low resistance.
The invention also relates to a method for determining the resistance and the reactance of dipoles (Zkm, Zkk) of a damping device for a cable having a plurality of wires, wherein the damping device has a plurality of first terminals to which the voltage vector U1 is applied and at which the current vector I1 flows, wherein a wire of the cable harness is connected to every first terminal, a plurality of second terminals to which the voltage vector U2 is applied and at which the current vector I2 flows, wherein a wire of the cable harness is connected to every second terminal, a first plurality of dipoles Zkk whose first terminal is connected to the wire k and whose second terminal is connected to ground, and an optional second plurality of dipoles Zkm whose first terminal is connected to the wire k and whose second terminal is connected to the wire m.
The expression ground within the scope of this patent application also comprises a local ground, for example a housing ground or a shield ground or a housing shield ground.
The method comprises the step of determining the S parameters of the cable by way of a measurement or a computer-implemented calculation or simulation. S parameters can include the control parameters. The chain matrix A can be calculated from the S parameters. The S parameters can be determined by a commercially available network analyzer. The S parameter matrix can be converted into a chain matrix A by formulas which are known to a person skilled in the art. The following applies:
            A              _        _              =                            (                                                                                          A                                          _                      _                                                        11                                                                                                  A                                          _                      _                                                        12                                                                                                                          A                                          _                      _                                                        21                                                                                                  A                                          _                      _                                                        22                                                              )                ⁢                                  ⁢                  and          ⁢                                          (                                                                                          U                    1                                    _                                                                                                                          I                    1                                    _                                                              )                    =                        (                                                                                          A                                          _                      _                                                        11                                                                                                  A                                          _                      _                                                        12                                                                                                                          A                                          _                      _                                                        21                                                                                                  A                                          _                      _                                                        22                                                              )                ·                  (                                                                                          U                    2                                    _                                                                                                                          I                    2                                    _                                                              )                      ;The admittance matrix Y is determined by the following equation:Yw√{square root over (A21A12−1)}={ykm}, k,m=l, n;where A21 has as a unit an impedance and A21 has as a unit the admittance, which are each extracted from the chain matrix, and Yw is a modal admittance matrix. The resistance and the reactance of the dipoles Zkm, Zkk can be determined by the following equations:
      Z          k      ,      m        =      {                                                      -                              1                                  y                                      k                    ,                    m                                                                        ,                          k              ≠              m                        ,                                                                          1              /                                                ∑                                      i                    =                                          1                      :                      n                                                                                                                              ⁢                                                                  ⁢                                  y                                      k                    ,                    i                                                                        ,                          k              =                              m                .                                                        
The approaches to damping common-mode resonances and differential-mode resonances for networks or cables known in the prior art are based on a scalar formulation of the wave impedances without taking into account the intermediate effects of the impedances owing to a parallel connection of common-mode impedances and differential-mode impedances. The circuits used in the prior art do not form an entire matrix and cannot damp all the resonance modes. The inventor has recognized that this problem can be solved by modal formulation of the wave impedance which can be represented as a network.
The damping device which is disclosed can take into account the resonances and the modes of a cable or of a cable harness and ensures that the cable or the cable harness emits or receives less interference. The damping devices of the prior art have hitherto merely taken into account the properties of an electrical device that was damped, but have not sufficiently taken into account the cable harness or the cable.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.